Metal vapor electric discharge apparatus



Apnl 29; 1952 H. c. BERTELE METAL VAPOR ELECTRIC DISCHARGE APPARATUSFiled April 12, 1948 3 Sheets-Sheet 1 FIG. 2.

Hana Q. BRTELE April 29, 1952 H. c. BERTELE 2,594,851

METAL VAPOR ELECTRIC DISCHARGE APPARATUS Filed April 12, 1948 3Sheet,s5heet 2 IO F/G.5.

24- 2s 6 sq F/ j) HANS: C. BERTELE April 29, 1952 H. c. BERTELE METALVAPOR ELECTRIC DISCHARGE APPARATUS Filed April 12, 1948 3 Sheets-Sheet 5I I J i HANs C. BERTELE Affor Patented Apr. 29, 1952 UNITED METAL VAPORELECTRIC niscmmeu APPARATUS Hans Carl Bertele, Purley, EnglandApplication April 12, 1948, Serial No. 20,424 In Great Britain April 17,1947 Clain1s. (01. 313-29) This invention relates to metal vapourelectric discharge apparatus, and more particularly to mercury vapourrectifier valves of the arc type including a cathode formed by a pool ofliquid mercury.

In such apparatus it has been found necessary to provide considerablygreater space Within the envelope than Was required to accommodate theelectrodes and the arc path, and this factor has increased both the bulkand weight and consequently the cost of the apparatus. The need for suchadditional space within the valve envelope is due to intense evaporationof mercury caused by heating at the arc spot.

Various proposals have been made for distributing the are spot in vapourdischarge apparatus by means of spot anchoring elements and proposalshave also been made for enhancing the cooling of the cathode pool bybathing the pool container externally with a liquid coolant or bycooling the anchoring elements by means of heat dissipatingarrangements. Applicant has now discovered that, with an are spotdistributed around the periphery of a pool container the metal wallwhereof has a thickness of the order of 0.5-2 mm. according to thethermal conductivity of the metal used, extended heat dissipatingsurfaces can be provided for such container in contact with a coolingmedium and will effectively prevent undue rise of temperature in thecathode and enable satisfactory operation to be accomplished. In effectapplicant achieves adequate reduction of mercury evaporation byarranging for extremely paths resulting in a low heat flow resistance between the cathode spot and the coolant, which resistance is lower thanhitherto.

The present invention thus provides improved valve arrangementsincluding effective cooling means for the mercury at the arc spotwhereby the evaporation therefrom, and consequently the necessary sizeof envelope is reduced.

In a vapour electric discharge apparatus according to the inventionincluding a cathode formed by a pool of vaporisable liquid metal foremitting an arc discharge, the are spot is extended around and anchoredto the upper peripheral edge of the cathode pool by formingthe innersurface of the pool container at such peripheral edge of an arcresisting metal which is wetted by the cathode liquid to produce aconcave meniscus while not being sputtered by ion bombardment therefromunder the operating conditions, and a short heat transfer path of g theorder of 0.5-2 mm., resulting in a low heat short heat transfer flowresistance, is provided between the containing surface at suchperipheral edge and a heat dissipating surface or member external to thepool container in contact with a cooling medium.

In the'practice of the invention as applied to mercury pool cathodes, asuitable arc resisting metal such as molybdenum or tungsten which iswetted by the mercury is used for the manufacture of the pool containeror provided as a linin strip to its inner peripheral surface around themeniscus of the mercury pool, and it will be understood that the arcwill become anchored to. such peripheral area by its natural tendency toseek the edge of the mercury meniscus and remain anchored to the wettedsurface.

The container is externally shaped to form fins or extended heatdissipating surfaces, or it has directly joined to it a member ormembers of high thermal conductivity material such as copper not itselfsuitable as a pool container material providing such extended heatdissipating surfaces. In either case, only an extremely short heattransfer path of about 0.5-2 mm, corresponding approximately to thethickness of the container wall, separates the heat dissipating membersfrom the are spot and with the wide distribution of the are spot therise in temperature thereat is minimised and the evaporation of themercury reduced or even eliminated. In one embodiment of the inventionthe mercury pool is contained in a steel cup having its inner surfacelined with molybdenum where it is in contact with the edge of themercury meniscus, and having bonded to its corresponding outer surface aring of high conductivity material such as copper formed with radiatingfins suitable for air cooling for instance by a fan placed underneaththe apparatus.

The area of the are spot may further be enlarged by providing theappropriate portion of the mercury container with a spongy lining of saymolybdenum or tungsten and/or a thin layer of oxide of either metal inplace of or in addition to the peripheral lining described, such asponge or oxide being adapted to retain or distribute the mercury at thewetting edge and spread the are over its surface.

Accordingly in a further embodiment the mercury container is providedwith a wide substantially horizontal annular flange having its inneredge. corresponding with the periphery of the meniscus of the mercurypool in a central well, while its upper surface is coated withmolybdenum sponge or oxide which retains mercury in its pores orinterstices. The underside of the horizontal flange is provided with anannular finned cooling member of copper so that, as in the previousembodiment, the heat transfer path to the cooling member is no longerthan the thickness of the mercury container wall.

The invention will be further described with reference to theaccompanying drawings where several embodiments are illustrateddiagrammatically by way of example and in which:

Fig. 1 shows a known arrangement of glassenvelope rectifier employing anarc-fixing device in the middle of the cathode pool, while Figs. 2 to 5show the improved cathode arrangements according to the inventionemploying a metal cup sealed to the glass envelope or body of arectifier.

Figs. 6 and 7 illustrate the application of the invention to valveshaving steel bodies respectively with and without metallic contactbetween said body and the cathode.

Fig. 8 shows a pool container provided with an annular flange forspreading the arc.

Fig. 9 showing a cathode pool container formed with an annular troughfor the mercury and having a supplementary arc-fixing surface, and

Fig. 10 showing a combination of a central pool with an annular troughand a supplementary arcfixing surface.

Referring now to the drawings and first more particularly to Fig. 1, amercury vapour rectifier valve of a known type, selected as an exampleof the class of apparatus with which the invention is concerned, isshown having a glass envelope l formed with a plurality of lateral arms2 each carrying an anode such as 3. The lower portion of the envelope 1is formed as a container 4 for a mercury cathode pool 5. In such knowntype of valves an arc-fixing device is sometimes employed inside thepool, and in the example shown a helical strip 6 of molybdenum ortungsten is immersed in the centre of the pool for this purpose and issupported on a metal rod 1 which passes through the bottom of thecontainer 4 to act also as the cathode lead for connection to theelectric circuit. The valve is mounted on a carrier 28 under the poolcontainer 4 and a fan or blower 9 is provided for eifecting cooling ofthe lower part of the valve. The degree of effective cooling however islimited in view of the poor heat conductivity of the glass container 4and the relatively lon heat path between the arc fixing device 6, wherethe arc-spot is anchored during operation, and the air-cooled outersurface of the container 4.

In the succeeding Figs. 2 to 10 which illustrate the present invention,the lower portions of the envelope 1 are shown, and the: cathode leadand fan or other optional circulating device are omitted for simplicity,and in Figs. 2 to 5 and 7 to 10 the upper part of the envelope and theanode or anodes are also omitted.

In Fig. 2 there is shown a simple application of the invention wherein amolybdenum or tungsten cup or pool container 4 is sealed to the loweropen end of a glass envelope I and is provided with integral radialradiating fins 8 for air cooling with or without the aid of a fan. Theare spot will settle at, and be extended around, the edge of the mercurymeniscus, which is illustrated at 5a, and there is an extremely shortheat transfer path from the location of the are merely through thethickness of the wall of the cup 4 to the heat disseminating outersurfaces of the cup and the fins 8.

In the modification shown in Fig. 3 the radial fins 8 are formed on aseparate ring to of a good heat conductor such as copper which is bondedto the molybdenum or tungsten cup 1 with a maximum area of contact. Thecup '4 in this example is preferably drawn or pressed from sinteredmolybdenum or tungsten sheet.

In the embodiment of Fig. 4 a molybdenum or tungsten pool container 4 islined with a ring 12 of the same material in a spon y form and/or coatedwith oxide for distribution of the mercury at the pool edge andconsequent better spreading of the are spot. No fins are shown in thisexample, and a finned ring Ii] similar to that shown in Fig. 3 may beprovided and/or cooling by forced circulation of air or water maysuitably be applied.

Fig. 5 shows a combination of the finned copper ring iii of Fig. 3 withthe molybdenum or tungsten sponge or oxide liner of Fig. 4, the metalpool container 4 being sealed, as in Figs. 2 to 4, to a glass envelopeI.

In the arrangement shown in Fig. 6 a steel envelope I is formed at itslower end as a cup or container 4for the mercury pool 5 and is pro videdat the wetting edge of the pool 5 with a molybdenum or tungsten liner 1?and with an external copper ring 50 finned at 8 as in the embodimentshown in Fig. 5. Since in this case the cathode system is not insulatedfrom the metal envelope I, an internal insulating lining or ring i3 isprovided above the liner 12 to prevent the cathode spot riding up thewalls of said envelope.

In the construction shown in Fig. 7 a total steel clad valve body I isformed at its lower end as a cooling jacket [4 for a molybdenum ortungsten pool container 4 which in this case is mounted within, andinsulated from, the body I by a pressure tight insulating ring l5 formedby glass moulded in situ. The jacket I4 is provided with an inlet i! andoutlet l8 for the circulating fluid cooling medium which may be air orliquid accordin to the electric currents involved and is passed underpressure through the space between the container 3 and the jacket wall.To prevent accidental metallic contact between the cathode and the bodyi due to mercury deposits on the glass of the ring IS, a cylindricalshield I5 is formed on the latter and is provided with an inwardlyprojecting annular flange 19.

In a further embodiment shown applied to a glass envelope valve in Fig.8, in place of the liner 12 the mercury container 4 is provided with awide substantially horizontal annular flange 23 having its inner edgecorresponding with the periphery of the meniscus of the mercury pool ina central well 2|, while its upper surface is coated with spongymolybdenum or oxide 22 which retains mercury in its pores or intersticesand thus distributes the are over such annular member. The underside ofthe horizontal flange 2B is provided with an annular finned coolingmember H) so that, as in the previous embodiments, the heat transferpath to the cooling surface is as short as the mere thickness of thewall of the mercury container.

In the construction shown in Fig. 9 the bottom of a molybdenum ortungsten pool container 25 is formed with a frusto-conical centralupward projection 25 the flat top of which is coated with molybdenum ortungsten sponge or oxide 26 and is arranged to be approximately at thesame height as the surface of the mercury pool 5. A. thin film ofmercury is held in the interstices of the sponge or oxide 26 which actsas an auxiliary arc-fixing surface additional to the peripheral wettededge 5a of the surface of the container 24 when the electric currentexceeds a given intensity. A copper ring or cup 30 is bonded to theoutside of the container 24 and the projection 25 and is provided withcooling fins B.

A similar arrangement is shown in Fig. 10, the additional arc-fixingsponge or oxide surface indicated at 36 being in this case of annularform and being located at the top of an annular boss 35 formed on thebottom of the molybdenum or tungsten pool container 34. As in theprevious embodiment, a copper ring or cup 40 fits over, and is bondedto, the outer surfaces of the container 34 and its annular boss 35 andhas integral cooling fins 8.

It will be understood that in the constructions shown in Figs. 9 and alining of sponge or oxide may be provided at the outer periphery of themercury meniscus 5a as shown at l2 in Figs. 4 to 6 and described inconnection therewith.

While the constructions having cooling fins are primarily suited for aircooling with the aid of a fan placed preferably beneath the valve, itwill be appreciated that, particularly where very heavy currents areinvolved, the fins may be surrounded by a jacket for either forced orthermosiphonic circulation of a liquid cooling medium.

By this invention, owing to the extension of the are spot and theshortening of the heat transfer path to the external cooling means,smaller, simpler and more economical electric discharge apparatus for agiven power output are obtained wherein internal cooling means may bedispensed with as well as the bafiies normally employed to deflect fromthe anodes the jets of vapour produced by evaporation at the are spot.

Furthermore, the present invention is applicable to liquid cathodeelectric discharge apparatus for any of the purposes for which they aresuitable and having a lass, metal or composite envelope containing anynumber of anodes with or without grids or other additional electrodes,it being understood that the term liquid cathode refers to theconditions obtained during operation of the apparatus and thereforeincludes substances other than mercury which are normally solid but areliquified at the operating temperatures of the discharge apparatus.

Finally, by reducing or eliminating the evaporation of the cathodeliquid during operation, the arc path to the anode or anodes may also bereduced with corresponding improvement in the efficiency of the valve.

What I claim is:

1. In vapour electric discharge apparatus the combination with anenvelope containing an anode, of a cathode formed by a pool ofvaporisable liquid, a container for such pool constituting a lower partof said envelope and formed at the upper peripheral-edge of said poolwith an arc-fixing surface of a metal of the group of arc-resistingmetals constituted by molybdenum and tungsten, which liquid bathes themetal arc-resisting surface to form a concave meniscus edge thereat, andare heat dissipating means external to the pool container in direct highthermal conductivity metallic connection with the arc-fixing surface.

2. Vapour electric discharge apparatus according to claim 1 including apool container of ferrous metal having the arc-fixing surface providedby an internal coating of the arc-resisting metal.

3. Vapour electric discharge apparatus accord"- ing to claim 1 havingthe surface at which the arc is fixed provided by an internal coating ofsponge of the arc-resisting metal on the cathode pool container.

4. Vapour electric discharge apparatus according to claim 1 having thesurface at which the arc is fixed provided by an internal coating ofoxide of the arc-resisting metal on the cathode pool container.

5. Vapour electric discharge apparatus according to claim 1 having theheat dissipating means provided as external cooling fins on the poolcontainer.

6. Vapour electric discharge apparatus according to claim 1 having theheat dissipating means.

provided as external cooling fins formed on a ring of good heatconducting material bonded to the external surface of the poolcontainer.

7. In vapour electric discharge apparatus according to claim 1,including a metal envelope, a downward extension of the lower portion ofsuch envelope formed as a spaced jacket around the pool container forthe circulation of cooling medium, and a gas-tight ring of insulatingmaterial between the container and such jacket.

8. In vapour electric discharge apparatus according to claim 1, acentral well in. the pool container within an annular flange having itsinner edge corresponding with the upper peripheral edge of the liquid ofthe pool, and a lining of sponge of the arc-resisting metal on the uppersurface of said flange operative to retain a film of the liquid anddistribute the arc-spot thereon.

9. In vapour electric discharge apparatus according to claim 1, acentral well in the pool container within an annular flange having itsinner edge corresponding with the upper peripheral edge of the liquid ofthe pool, and a lining of oxide of the arc-resisting metal on the uppersurface of said flange operative to retain a film of the liquid anddistribute the arc-spot thereon.

10. In vapour electric discharge apparatus according to claim 1, anadditional cooled arc-fixing surface of the arc-resisting metal locatedwithin the pool at the level of the upper surface of the latter.

11. In vapour electric discharge apparatus according to claim 10, acentral upward projection from the bottom of the pool container the topsurface of which constitutes the additional arcfixing surface and iscoated with sponge of the arc-resisting metal to retain a thin film ofthe cathode liquid.

12. In vapour electric discharge apparatus the combination with anenvelope containing an anode, of a molybdenum container for a cathodepool, a portion of which container also acts as an arc-fixing structure,and metallic means having heat dissipating surfaces on the outside ofsaid portion of the container in contact with a gaseous cooling medium.

13. In vapour electric discharge apparatus the combination with anenvelope containing an anode, of a tungsten container for a cathodepool, a portion of which container also acts as an arcfixing structure,and metallic means having heat dissipating surfaces on the outside ofsaid portion of the container in contact with a gaseous cooling medium.

14. In vapour electric discharge apparatus the combination with anenvelope containing an anode, of a cathode formed by a pool ofvaporisable liquid in a lower part of said envelope, a container forsuch pool formed at the upper periphand pool edge with an arc-fixingsurface of a metal of the group of arc-resisting metals constituted bymolybdenum and tungsten bathed by the liquid, and are heat dissipatingmeans external to the pool container in direct high thermal conductivitymetallic connection with the arc-fixing surface through a heat transferpath less than two millimetres in length.

15. A vapour-electric device comprising, a metal container, an anode inspaced insulated relation in said container, a pool of vaporisablereconstructing cathode material in said container and a layer of spongerefractory metal in said container.

HANS CARL BERTELE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,757,605 Ulrey May 6, 19302,137,836 Elder Nov. 22, 1938 2,431,153 White Nov. 18, 1947 2,432,513Depew Dec. 16, 1947 2,468,037 Clark Apr. 26, 1949 2,490,087 Pakala Dec.6, 1949

